Hypothyroidism is one of the most common endocrine diseases affecting dogs and results when the thyroid gland doesn’t produce and secrete enough thyroid hormones. The thyroid gland is located in the mid-neck region near the larynx. Hormone imbalance in dogs is usually caused by inflammation or contraction of the thyroid gland. This progressive destruction of the gland leads to reduced thyroid function and inadequate levels of thyroid hormones. 

There are two forms of primary hypothyroidism in dogs: lymphocytic thyroiditis and idiopathic atrophy. Lymphocytic thyroiditis is an immune-mediated disorder that appears to have a genetic component based on breed predisposition for the disease. The body’s immune system develops antibodies against its own thyroid gland because of an over-reactive immune response. Its process is characterized by chronic and progressive lymphocytic infiltration and destruction of the thyroid gland. This process is slow and leads to the gradual onset of clinical signs associated with hypothyroidism. Idiopathic atrophy of the thyroid gland may be a primary degenerative disorder or an end stage of lymphocytic thyroiditis. It is a different form of thyroid destruction that does not have an inflammatory component, but is caused by the replacement of normal thyroid tissue with adipose tissue. Together, these two account for 95% of the clinical cases of hypothyroidism in dogs.

Diagnosis of Hypothyroidism:

Diagnosis of Hypothyroidism can be done through physical examination, routine blood & urine tests, and tests of thyroid gland function i.e. T3, T4 and TSH. Increased cholesterol, triglycerides and lipemia are classic clinical chemistry findings in dogs with hypothyroidism. There is also a generalized decrease in cellular metabolic activity.  28–32% of hypothyroid dogs also demonstrate anemia.

Common signs of Hypothyroidism in Dogs:

  • Hair loss on the back, legs & tail is common. Dermatological abnormalities, dry & lackluster coat, flaky skin, black patches, excessive shedding etc can also be observed in dogs with underactive thyroid.
  • Lethargy & weight gain are the most common signs reported by dog parents. Slowing of cellular metabolism also results in mental dullness and exercise intolerance in dogs. 
  • Seborrhea (scaly patches & red skin), Pyoderma, brittle coat etc can be observed. Chronic changes to the skin can result in thickening and hyperpigmentation.
  • A tendency to gain weight and development of hyperlipidemia are two problems associated with untreated hypothyroidism that may require dietary intervention. Weight gain occurs in dogs even without any increase in food intake.  
  • Difficulty in maintaining body temperature will make the dog intolerant towards cold temperatures.
  • Myxedema (aka tragic face) results in puffiness on forehead and drooping of eyelids. 
  • Other signs include – gut distress, constipation/diarrhea, slow heart rate, depression, aggression, muscle weakness or atrophy, stiffness, dry cough etc. 

Dietary management:

Most cases of Thyroid dysfunction are not nutritional deficiency related. They are related to imbalanced immune system, inflammation and/or triggered autoimmunity. However, hypothyroidism can be managed through a balanced diet which will help improve the dog’s immunity. 

  • Gut Health – The first step in treating any immune related condition is to target gut health. Immunological reactions lead to inflammation in the gut, which makes the hypothyroidism worse. Leaky gut, dysbiosis, poor stomach acid are all common in dogs with hypothyroidism. Probiotics are live beneficial microorganisms that promote a healthy balance of bacteria in your dog’s gut. Probiotic foods such as curd, kefir, fermented vegetables etc will help keep your dog’s gut healthy. OTC probiotics with lactobacillus strains and enzymes are also effective in restoring gut health. 

  • Anti-inflammatory food – Reducing inflammation is key to managing hypothyroidism in dogs and anti-inflammatory foods help reduce markers of inflammation. Aim to feed overall healthy food and a balanced diet, and add anti-inflammatory whole food ingredients such as turmeric, fatty fishes, green leafy vegetables (in moderation), broccoli, flaxseeds or flaxseed oil, olive oil, turkey tail or shiitake mushrooms, bone broth etc. A homecooked diet that is balanced to include all essential vitamins & minerals also act as an anti-inflammatory agent.  
  • Optimize Omega 6 & 3 fatty acid balance – Excessive amounts of omega-6 polyunsaturated fatty acids (PUFA) and a very high omega-6/omega-3 ratio promote the pathogenesis of many diseases, including cardiovascular disease, cancer, and inflammatory and autoimmune diseases, whereas increased levels of omega-3 PUFA (a low omega-6/omega-3 ratio) exert suppressive effects. An Omega-6 to Omega-3 ratio of 2-3/1 helps suppress inflammation. The therapeutic dose of omega-3 fatty acids will depend on the degree of severity of inflammation & dysfunction. Omega-3 rich food sources that you can add to you dog’s diet are fatty fishes, fish oil, cod liver oil etc
  • Antioxidant rich food – Antioxidants protects tissues from damage and help counter oxidative stress. Vitamin C, is an essential vitamin that plays a huge role in immunity and inflammation. Feeding a diet rich in antioxidants will help manage hypothyroid induced systemic inflammation. Food sources – blueberries, gojiberries, kale, raspberries, red cabbage, red bell peppers, radish, lettuce etc
  • Iodine – Iodine can help when your dog’s body doesn’t make enough thyroid hormones. Kelp supplements are a good source of iodine, and should be added to homecooked meals only as prescribed by a Nutritionist or Vet. 
Stress is another factor that affects immunity. As with humans, hypothyroidism in dogs manifests as impaired mental function and anxiety. Stress alone will not cause a thyroid disorder, but it can make the condition worse. The impact of stress on the thyroid occurs by slowing your dog’s metabolism. Engaging dogs in regular mental and physical stimulation exercises can help manage their stress. Physical activities like walking, playing fetch, enrichment toys can help your dog release tension. It is also good to provide your dog with a safe place in the home where he can escape anxious situations.

Avoid excessive use of antibiotics, steroids, NSAIDs etc as these drugs can trigger inflammation and make thyroid dysfunction worse. Endocrine system is closely interconnected and any disorder affecting other glands (pituitary, adrenal), or hormones (like insulin) will affect thyroid function. In case of comorbidities, dietary intervention is done keeping in mind nutritional requirement of additional conditions also. Skin and coat changes, as well as obesity, can take much longer to resolve, up to several months. A balanced well formulated diet by a Nutritionist will help meet your dog’s nutritional needs and manage the disorder & symptoms in a holistic way.